Japanese Patent Publication No. 04-147595 discloses a fixing heater, for a copying machine, comprising an electrically conductive powder such as a powder of silver, silver/palladium, carbon powder, etc., bound with a synthetic resin to form a heating element on a substrate. The surface of the heating element is covered by a glassy protecting film to help the object to be heated to slip and to prevent wear of the heating element.
Japanese patent Publication No. 07-160132 discloses a heating device, in a film heating system, comprising a heating element formed by sintering a compound of transition metal elements such as Mn, Ni, Fe, etc., so as to exhibit a negative temperature coefficient (NTC) in order to use the NTC characteristics to control the temperature of the heating element itself.